Why Is My Calculation of Net Torque Incorrect?

[jghlee]

Homework Statement

This is the problem: http://session.masteringphysics.com/prob ...

A squar emetal plate .180 m on each side is pivoted about an axis through point O at its center and perpendicular to the plate. Calculate the net torque about this axis due to the three forces shown in the figure if the magnitudes of the forces are F1=18.0n, F2=26.0N, and F3=14.0N. The plate and all forces are in the plane of the page.

The Attempt at a Solution

Okay so this problem looks simple enough... but I get the wrong answer.

So here's what I did. I individually calculated the torques for each force.

Torque for F1: (18.0)(.09)=1.62
Torque for F2: (26.0)(.09)=2.34
Torque for F3: (14.0)(sin45)(.09)=.89095

Then I find the net torque by...
-F1+F2+F3=1.61N m

but the answer should be 2.5N m.

Can anybody tell me what I'm doing wrong?

 

[tyco05]

I can't open your link.

 

[tiny-tim]

Welcome to PF!

Torque for F1: (18.0)(.09)=1.62
Torque for F2: (26.0)(.09)=2.34
Torque for F3: (14.0)(sin45)(.09)=.89095

Then I find the net torque by...
-F1+F2+F3=1.61N m

but the answer should be 2.5N m.

Hi jghlee! Welcome to PF!

I can't see the picture (you've chopped off the end of the url ) …

but since you're exactly 0.89 out, my guess is that you've multiplied by sin45º instead of dividing by it!